Many Internet alcohol vendors are lax at verifying that customers are of legal age, making it easy for teens to buy alcohol, according to a new study.

Researchers at the University of North Carolina at Chapel Hill asked eight volunteers between the ages of 18 and 20 to attempt to purchase alcohol from 100 of the most popular vendors using prepaid gift cards.

Nearly 60 percent of companies selling alcohol online made little, if any, effort to verify customers' ages.  Of 45 successful orders, 51 percent didn't use any type of age verification.

But the researchers also placed blame on the delivery companies, despite corporate policy that age verification is required for wine shipments.  Wine is the only alcoholic beverage that the shipping companies - FedEx and UPS in this study - will ship as per their regulations.

"Some packages were left at the door, or handed to recipients after checking an underage identification or simply asking if the person receiving the package was 21," said Rebecca Williams, the study's lead author at a research associate at the University of North Carolina Center for Health Promotion and Disease Prevention in Chapel Hill.

Driver's licenses given to anyone younger than 21 are clearly marked in N.C., making anyone younger than the legal drinking age easy to identify.

Williams added that parents should also be aware of how easy it is to purchase alcohol online, and how easy it is for teens to obtain and use a parent's driver's license.

"Teens widely report having access to parents' identifications and having no qualms about using them to bypass age verification," Williams explained.  "Children can also hide online purchases from parents by using prepaid cards they can buy with cash."

In response to the study findings, a spokeswoman for UPS, who has not yet reviewed the study, stressed to ABC News that company policies regarding alcohol shipments are very strict.

"UPS procedures are put in place to reduce the risk that any minors would have access to illegal alcohol," she said.  "If UPS is involved in deliveries containing alcohol, the delivery person would need to secure an adult signature."

The spokeswoman also explained that wine delivered through UPS must have a sticker on the package that indicates an adult signature is required as part of the company's wine shipping program that only allows approved vendors to ship wine.

A spokesman for FedEx said the company doesn't condone the sale of alcohol to anyone underage and has policies in place to prevent it from happening.

"We take the findings in this report seriously. After we have had time to review the study, we will take any necessary corrective action to ensure our policies are being followed," said company spokesman Scott Fiedler.

Williams said the study provides evidence that illegal alcohol sales are a significant problem.

"Part of why this problem exists is because there is little regulation to restrict online alcohol sales," she said.